“When the King “wiped away” the debt— using the precise Greek word relating to debts and not sins— he wiped away all debts connected to that debt— he didn't do a solid for the servant and give him a 0 in the liabilities column and +100 in the assets column. It wasn't merely a good idea or a noble gesture that the servant in turn forgive servant 2's debt. That debt no longer existed. The servant's crime, therefore, wasn't in not being merciful but in lying, tricking the other servant into believing a debt existed when one did not.
The next question then becomes: why didn't servant 1 “forgive” servant 2's debt— why did he insist— pretend— lie— there was a debt when there was none? Greed does not explain it, the timing is there before you: how badly does he need 100 denarii right now, suddenly and out of the blue, when he was content merely to be owed this money all that time before? For orientation note that 100 denarii is three months wages or 2500 loaves of bread, or a third of a bottle of perfume, it's a weird economy, anyway— did he actually think he was going to get paid immediately? He wasn't unmerciful, he was enraged— because he was shown mercy, because the mercy that was shown to him was a kind of enslavement: when his monetary debt was waived, he owed a different debt to the King; with the cash debt gone another debt overwhelmed him, he owed a debt with his entire existence, his soul. The kingdom of heaven is like a certain king of men who wanted to settle accounts. This debt can never be paid back, and how one lives with such a debt determines... how one lives with such a debt. The servant couldn't live with it, his brain collapsed into a black hole. That kind of infinite dependency to the King was intolerable. To him, far from the debt being a new kind of freedom grounded in a new kind of duty— the debt meant madness.”